Audi's Multitronic CVT

A bold step forward in stepless transmissions.

We've seen Continuously Variable Transmissions before from automakers like (Justy) and (Civic HX), admired them in concept, but criticized them in practice. There were problems: These CVTs can't transmit much torque, limiting their use to smaller 3- and 4-cylinder cars. And worse, in operation they feel like a conventional manual gearbox with a horribly worn clutch, where engine revs soar above road speed, with road speed eventually catching up. Disconcerting, to say the least.

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Audi has addressed these problems with its Multitronic CVT, paired with its all-new 220-bhp 3.0-liter V-6 that's available in both the and (see Ampersand, September 2001). Handling its peak torque of 221 lb.-ft. is the Multitronic's link-type chain. Manufactured by Luk, the 1025-link, 1.4-in.-wide, 3.7-lb. chain operates in tension, rather than compression as with the commonly used Van Doorne metal belt. And the clamping loads of the movable pulley halves are applied to the ends of the chain's 75 pairs of link pins, rather than to the edges of the Van Doorne belt's triangular steel plates that are strung together like a bead necklace.

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claims there's no slippage, even at the highest numerical ratio (12.7:1) where only nine pairs of link pins, made of ball bearing-grade steel, are clamped by the drive pulley. If a sudden shock to the driveline occurs, such as a wheel regaining traction after spinning on ice, a mechanical torque sensor instantaneously applies a clamping force — in addition to the normal hydraulic pressure — to prevent slippage. This approach allows the CVT's hydraulic pump to run at a reduced pressure, increasing efficiency.

Another potential power-sapper is a torque converter, which the Multitronic avoids by using two oil-cooled multi-disc clutches, one for forward, one for reverse. Controlled electronically, the clutch provides a bit of "creep" that's lessened when the brake is applied. Interestingly, there are other features within Multitronic's lightweight magnesium case that emulate conventional automatics: A Tiptronic sequential-shift feature allows clicking up and down through six "gears" that are actually just preset positions on the pulleys. And, more important, the throttle doesn't feel like an on/off switch.

With, say, an 80-percent throttle opening, the revs ramp up nicely with speed. It's only with foot-to-the-floor driving that rpm shoots straight to the torque peak for maximum acceleration. Going down a hill? The electronic controls subtly adjust the ratio for increased engine braking, slightly more if the brake pedal is applied. Up a hill? No hunting between ratios; just a shockless transition as the chain rises in one pulley's groove and descends in the other. In tests of European models, acceleration and fuel consumption were at least equal to models equipped with 5-speed manual transmissions.

Although a number of Japanese manufacturers have roller-type CVTs with high-torque capability for their home market, each depends on a specially formulated fluid to transfer the power through viscous shear. The Multitronic requires a less exotic lubricant that's similar to ATF, with a change interval of 60,000 km (about 37,000 miles). Audi obviously has confidence in its design, having offered it on the European A6 since October 1999, and being the first to offer such technology to U.S. consumers for 2002. Only front-drive versions will be sold at first; for an A4 or A6 Quattro Multitronic, you'll have to wait until at least 2004.